MS probably get the idea for App Store, from Apple-Store or Sony's PSN. More updated version of search Web for non-registered extension, but instead letting user search in wild-web, Microsoft has done it for users (with a price). To milks more money from the users, visiting the Microsoft App-Stores might be the default action, instead of classic action to look for programs in user' harddrives. I bet my two cents, that MS will not make it easy to change suggested the app-store vendor (from MS app-stores to another), just incase some independent vendor decided to setup their own app-stores.